Many types of instruments, devices, appliances and the like including, for example, surgical and other medical instruments (collectively “instruments”) must be sterilized prior to use. Typically, such instruments are packaged, sealed and sterilized in disposable packaging so they can be safely transported and stored until they are used. Several sterilization techniques are known in the art, including gamma radiation, steam, dry heat and ethylene oxide sterilization techniques. In general, a sterilizing gas, vapor or liquid flows through pores in the disposable packaging and sterilizes the instruments contained therein. The sterilizing gas, vapor or liquid dissipates from the package also through the package's pores.
To form such a disposable package, an instrument may be placed between two layers of paper or plastic substrate, at least one of the layers being impervious to bacteria and debris while also being permeable to gases or steam, and the layers are sealed together to form a bag or pouch. A pouch or bag may also be formed from a paper or plastic substrate prior to inserting an instrument therein with a flap at or near an opening in the pouch such that the flap may be folded over and sealed to the pouch with an adhesive or other type of known sealing method. Alternatively, an instrument may be placed in a paper or plastic tray, sometimes molded to the shape of the instrument, and then covered and sealed with at least one layer of paper or plastic substrate that is both impervious to bacteria and debris, and permeable to gases or steam.
Substrates useful to form such packaging should exhibit sufficient airflow through the material to relieve pressure in the package during sterilization, high steam permeability, resistance to high temperatures, and should provide a significant barrier to penetration by bacteria and debris. It is also desirable that a substrate for this purpose be flexible, strong, printable, and sealable to itself and thermoplastic films and substrates. Other desired characteristics depend on the particular product disposed within the packaging.
An example of a commonly used medical packaging material is a high strength barrier nonwoven composed entirely of flash-spun polyolefin (usually high density polyethylene) sold under the trademark TYVEK® by E.I. DuPont De Nemours & Co. and described in U.S. Pat. No. 3,169,898 to Steuber. Although TYVEK® fabric is micro-porous and acts as a barrier to particulate matter that is sub-micron in size, TYVEK® fabric has very low air and gas permeability (i.e., high resistance to air and gas permeation), making the penetration of ethylene oxide and steam, and their subsequent off-gassing difficult and time consuming. TYVEK® fabric also has poor printability due to its inherent low surface energy and suppleness, and must be treated and/or coated to improve printability. Further, TYVEK® fabric has a relatively low melting point (approximately 130° C.) and will severely deform and shrink under high temperature sterilization techniques such as steam, which is typically conducted at temperatures greater than 135° C.
Barrier fabrics have been developed using wet-laid processing techniques, and often include 100% wood pulp, which is wet-laid on a Fourdrinier machine, saturated with latex and highly calendered. In the medical industry, these barrier fabrics are commonly referred to as “medical packaging paper.” Wet-laid barrier fabrics made from other fibers are disclosed in U.S. Publication No. US 2010/0272938 A1, published Oct. 28, 2010. However, wet-laid nonwovens typically do not have sufficient barrier properties to prevent bacteria and debris from penetrating through the fabric, and also lack sufficient strength for packaging instruments.
Barrier properties of a porous packaging material (i.e., the ability to resist the passage of microorganisms) are measured using ASTM Standard F1608, “Standard Test Method for Microbial Ranking of Porous Packaging Materials (Exposure Chamber Method),” and result in a “Log Reduction Value” for a material. The higher the Log Reduction Value, the more effective a material is at filtering out bacteria. For example, medical grade TYVEK® fabric has a Log Reduction Value of 5. Wet-laid nonwovens and papers typically have a Log Reduction Value between 1 and 2.5. Wet-laid nonwoven fabrics containing cellulosic fibers can improve their barrier properties by using highly refined pulps, calendering and/or selecting shorter and thinner walled hardwood fibers, but these modifications also weaken the physical strength (i.e., tear strength) of the fabric, reduce opacity and increase stiffness. Cellulosic fibers also tend to weaken and discolor during certain sterilization techniques such as steam and ethylene oxide sterilization.
It is therefore an object of this disclosure to overcome the foregoing difficulties such as those associated with TYVEK® medical grade fabric and cellulosic wet-laid nonwovens and papers, and provide a nonwoven substrate that exhibits high strength and that can withstand higher temperatures than TYVEK® medical grade fabric, is steam sterilizable, has sufficient airflow to relieve pressure in the package during sterilization, provides a significant barrier to penetration by bacteria and debris, is sealable to itself and thermoplastic films and substrates, and is printable.